Powerline Communicated Load Control

ABSTRACT

A system for transmitting communication signals, the system comprising an injector circuit connected to a powered circuit conductor and configured to modulate a power signal with a direct current voltage offset, the direct current voltage offset being within a range that causes approximately 1 percent or less total harmonic distortion of the power signal; and a decoder connected to the powered circuit conductor and a load, the decoder configured to demodulate the direct current voltage offset to control the load. A method for transmitting communication signals, the method comprising modulating a power signal on a powered circuit conductor with a direct current voltage offset, the direct current voltage offset being within a range that causes approximately 1 percent or less total harmonic distortion of the power signal; and demodulating the direct current voltage offset to control a load.

CROSS REFERENCE

This application claims priority to U.S. Provisional Application No.61/574,073, entitled POWERLINE COMMUNICATED LOAD CONTROL and filed Jul.28, 2011, the contents of which are incorporated herein by referenceinto the present application.

FIELD OF THE INVENTION

The invention relates to the technical of communicating control signalsover an AC supply line.

BACKGROUND

Throughout the civilized world there is a growing need to make moreefficient use of the supply of electrical power. With this increasinginterest in energy conservation, methods for centralized control ofelectrical loads that are uncomplicated and cost-effective to installare becoming more important. Using lighting loads as an example, oneeffective way to reduce energy consumption is to use dimmable lightingsystems. Newer lighting systems control light output and energyconsumption by adjustment of lighting levels throughout the day,reducing energy usage when light is not needed.

The growing imposition of time-of-day dependent utility rates presentsanother important economic rationale for curtailing consumption to avoidonerous penalties for excessive peak loads. As electric power generationcapacity becomes less able to meet periods of excessive demand,consumers are becoming more accepting of utility provisions toautomatically reduce load demands rather than experience a brownout.

Load control systems utilizing separate dedicated wiring have beenwidely employed for energy and comfort management in new commercialbuildings. However, costs of adding the required control wiring usuallyprohibits such load control upgrades to be retrofit to existingbuildings. A cost-effective wireless system would, however, mitigate thecomplications of the routing of new wiring that would be required.

Historically, remote load management was implemented through the use ofphysical control wires that interconnected an automatic or manualcontroller with each load (e.g. lighting fixture) under its control.However, when applied to lighting control, the requirement for newdedicated control wiring proved to be excessively costly in thoseinstances where lighting controls were to be added after the originalbuilding construction. And, even in the case of new construction,attractive reduction of installation costs can often be realized byutilizing the power wiring infrastructure as a communications medium forenvironmental building control signals.

Due to the considerable quantity of lighting fixtures that are employedin most buildings, it is important that the per-fixture cost of dimmingbe reduced as much as possible. To satisfy this requirement, severalwireless control communication techniques have been put into practice.One such approach uses dimming signals that are transmitted by phase-cutmanipulation of the power supplied to specially equipped fixtures on anexisting lighting branch. For example, Philips Advance Transformer MarkX® and Lutron TuWire® ballasts use phase cut manipulation. Typically,wall-mounted dimmers, such as those usually employed for incandescentloads, are then used for manual dimming control with phase cutmanipulation. This method has proved very convenient for small areas,but not for wide application because power quality is incrementallyreduced by each fixture under such control.

There has been a longstanding need for a reliable, low-cost means ofcommunicating load management commands in commercial applications. Useof the existing power lines for this purpose always seemed to offer avery attractive solution. The traditional approach to meet this goalattempted to use a variant of power line carrier control (“PLC”). PLCinvolves superimposing a coded carrier frequency in the range 100 kHz to2 MHz or a timed burst of noise onto the AC power line. Systemsemploying PLC have seen widespread use in residential lightingapplications, but limited penetration in commercial lightingapplications. Osram-Sylvania introduced a commercial PLC control systemfor demand response applications, under the designation of PowerSHED®.However, the system has yet to achieve significant market acceptance.

Still another general approach to remote load control uses radiofrequency signaling. For this approach, control messages in the form ofradio frequency signals are transmitted via a mesh network, where theyare handed off sequentially though low-power transceivers located ateach control point. However, a low-cost implementation of this approachcapable of communicating control messages has been illusive.

SUMMARY OF THE INVENTION

The present invention allows load control signals to be sent over thesame wiring that is used to provide AC power to the load. This isparticularly applicable to remote lighting control, where the additionof dedicated wiring for lighting control can be costly and timeconsuming. By using the existing AC supply wiring, the changeover fromconventional lighting to is greatly simplified and installation costsare significantly reduced.

Although the controlled diming of light fixtures has been described inthe preceding paragraphs as a typical example of an application ofpowerline communicated load control, many other applications areanticipated. Examples include the management of heating, ventilation andair-conditioning (HVAC) loads, window shade controls, appliance plugload controls, light emitting diode color mixing, and hot water heating.

In one form, the present disclosure provides a system for transmittingcommunication signals over a powered circuit conductor. The systemcomprises an injector circuit connected to a powered circuit conductorand configured to modulate a power signal with a direct current voltageasymmetrically resulting in a DC offset, the direct current voltageoffset being within a range that causes approximately 1 percent or lesstotal harmonic distortion of the power signal; and a decoder connectedto the powered circuit conductor and a load, the decoder configured todemodulate the direct current voltage offset to control the load.

In another form, the present disclosure provides a method fortransmitting communication signals over a powered circuit conductor. Themethod comprises modulating a power signal on a powered circuitconductor with a direct current voltage asymmetrically resulting in a DCoffset, the direct current voltage offset being within a range thatcauses approximately 1 percent or less total harmonic distortion of thepower signal; and demodulating the direct current voltage offset tocontrol a load.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description, including disclosedembodiments and drawings, are merely exemplary in nature intended forpurposes of illustration only and are not intended to limit the scope ofthe invention, its application or use. Thus, variations that do notdepart from the gist of the invention are intended to be within thescope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to appreciate the manner in which the advantages and objects ofthe invention are obtained, a more particular description of theinvention will be rendered by reference to specific embodiments thereofwhich are illustrated in the appended drawings. Understanding that thesedrawings only depict preferred embodiments of the present invention andare not therefore to be considered limiting in scope, the invention willbe described and explained with additional specificity and detailthrough the use of the accompanying drawings in which:

FIG. 1 is a block diagram for installation of the power linecommunicated load control system in a single lighting branch;

FIG. 2 is a block diagram for installation of the power linecommunicated load control system in multiple lighting branches;

FIG. 3 is a schematic for an injector circuit in accordance with oneaspect of the invention;

FIG. 4 is a schematic for an injector circuit accordance with an aspectof the invention;

FIG. 5 is a schematic for an injector circuit in accordance with anaspect of the invention;

FIG. 6 is a schematic for an injector circuit in accordance with anexemplary embodiment;

FIG. 7 is a schematic for a decoder circuit in accordance with an aspectof the invention;

FIG. 8 is a flow chart showing a method for decoding control signals ona powerline in accordance with the disclosed principles.

FIG. 9 is a schematic for an isolation interface for a decoder circuitin accordance with the disclosed principles.

FIG. 10 is a block diagram for adapting PCLC to a light fixture having a0-10 volt analog ballast or voltage-controlled dimming LED driver;

FIG. 11 is a block diagram for adapting PCLC to a light fixture having aPWM controlled dimming LED driver or current control;

FIG. 12 is a block diagram for adapting PCLC to a light fixture having atwo-wire dimming fluorescent ballast.

FIG. 13 is a block diagram for adapting PCLC to a light fixtureconfigured to operate with a three-wire dimming control; and

FIG. 14 is a block diagram for adapting PCLC to a light fixtureconfigured to operate with a DALI dimming control.

DETAILED DESCRIPTION

The present invention provides a new system and method for communicatingload control signals on existing branch power lines. Known systems forsending control signals over power lines employ the injection of carriercurrent signals having a frequency of 100 kHz and higher. Theserelatively high frequency signals are difficult to propagate over 50 or60 Hz power lines with their associated loads. One aspect of the presentinvention is to utilize low-frequency supply voltage as a carrierfrequency and then modulate the supply voltage signal in accordance withthe information to be communicated. Although this approach provides acommunication bandwidth of only a fraction of a cycle per second, suchspeed is adequate for the intended load management application. Thistechnique is referred to as Power line Communicated Load Control(“PCLC”).

PCLC can be used for on/off control of incandescent, fluorescent, lightemitting diode (“LED”), high intensity discharge (“HID”) and inductionlighting sources. It can also be used to manipulate the dimming level ofany of the above light sources that have been equipped for dimming.Although the preferred embodiments will be described in the context oflighting in commercial buildings, it should be understood that PCLC canbe applied to all types of fixed electrical loads.

The PCLC system preferably performs at least two load control actions;load shave and load shed. Load shave refers to trimming non-essentialcomponents of the total load during periods of the day when theapplicable electric rate is at a premium, or during intervals whenexcessive consumption can trigger an onerous rate escalation forexceeding a prescribed level of peak demand. Load shed refers to aresponse to an indication from the serving utility that it will beexperiencing a period of critical capacity shortage during specifiedupcoming intervals. Such a response may be elective, in order to helpavoid a system-wide “brown out” or may be mandatory if the consumer haspreviously agreed to such a response in return for a favorable billingrate.

PCLC has a number of benefits when applied to lighting applications.First, PCLC produces minimal disturbances of the AC power quality bymaintaining high power factor and low harmonic distortion of the ACpower line current. Second, PCLC is capable of sending commands down apower line in such a way that they are uniquely confined to thedownstream physical limits of that power line. This prevents anyundesired command signal bleed onto other lighting branches. Finally,PCLC represents a cost effective way to implement remote lightingcontrol in existing construction that is already not fitted withseparate dedicated wiring for lighting control.

FIG. 1 is a block diagram for PCLC as installed on a single lightingbranch. As seen in FIG. 1, PCLC is preferably comprised of an injector101, a system control 102, and a decoder 103. When load control isdesired, the system control 102 connects the injector 101 to the networkin order to introduce a voltage asymmetry on the AC line conductor. Whenno signaling is in process, the injector 101 is disconnected from thenetwork so as to be lossless. By enabling the asymmetry condition in anon/off pattern, coded control signals can be sent down the AC lineconductor. The voltage asymmetry on the AC line conductor manifestsitself as the presence of a DC bias or offset that is within a rangethat causes approximately 1% or less total harmonic distortion of thepower signal. Preferably, the DC offset is within the rage of 1 to 5volts. Downstream loads are equipped with a decoder 103 to detect thesignals introduced by the injector 101 onto the AC line conductor. Thedecoder 103 decodes the voltage asymmetry into the desired command foruse by the load.

The injector 101 is installed in series with the AC line conductor thatsupplies the controlled load. Because the injector 101 is installed inseries with the AC line conductor, the AC line conductor must be openedfor installation. The injector 101 is installed at a point on the ACline conductor that is in series with all the loads over which PCLC isto exert control. In one aspect, the injector could be installed inseries with either an entry wall switch or at a junction box for controlof electrical loads in a single room. In another aspect, the injector101 could be installed at the circuit breaker for a branch circuitserving individual plug-in outlets. In another aspect, the injector 101could be installed in the AC line conductor entry to a distributionpanel 104, if all loads served by that distribution panel 104 are toreceive the same load control signals. In yet another aspect, theinjector 101 could be installed in the AC line conductor entering themain electrical supply panel for an entire facility, if all electricalloads in that facility are to receive the same load control signals. Inthis case, the injector 101 would preferably be scaled for a highercurrent capacity. FIG. 1 shows some of the locations at which theinjector 101 could be installed.

The system control 102 is typically wired to the injector 101 in orderto regulate the introduction of control signals on the power line.System control 102 can be installed in a number of locations. Forexample, system control 102 can be installed in a wall-mounted fixture104 outside the lighting panel as shown in FIG. 1. Alternatively, systemcontrol 102 may be installed in the lighting panel near the injector101. The system control 102 can originate from a number of sources,including, but not limited to: (1) a manual key-switch enabledcontroller; (2) a programmable time clock; (3) a controller thatmonitors real-time electric demand, to avoid onerous peak demandexcesses; (4) an Ethernet interfaced controller located on the premises;(5) an internet enabled remote control location; or (6) a building wideenergy management system.

Preferably, a decoder 103 is installed in each lighting fixture 105 inthe lighting branch to interpret the control signals on the AC powerline. Although FIG. 1 depicts the decoder 103 as separate from thelighting fixture 105, the decoder 103 can be installed within thelighting fixture 105 itself.

FIG. 2 shows installation of a PCLC system in a building with multiplelighting branches. Here, an injector 201 is installed for each lightingbranch. As discussed above in FIG. 1, the injector 201 is preferablyinstalled in the lighting panel 204, but may be installed in otherlocations as well. Each injector is fitted with two forms of systemcontrol 202 a and 202 b. System control 202 a is a switch installed in awall-mounted fixture and hard-wired to the injector 201. System control202 b originates from an internet enabled controller. System control 202b can be hard-wired to the injector or it may transmit signals to theinjector wirelessly. Although the injectors are being controlledidentically in FIG. 2, it may be important to control each lightingbranch independently in certain circumstances. It should be appreciatedthat PCLC can be adapted to function in a way that confines thesignaling specifically to each branch, by installing a separate injectorin each branch circuit. Because the injector delivers the control signalto only downstream components, no unintentional bleeding of the controlsignal across neighboring branches can occur.

FIG. 2 depicts a PCLC system where light fixtures 205 are groupedtogether and provided with an independent occupant control 206. Theindependent occupant control 206 can be, for example, a wall-mountedlight switch located proximal to the light fixtures 205. The independentoccupant control connects or disconnects the light fixtures 205 from thebranch supply line. When the independent occupant control 206disconnects the light fixtures 205 from the supply line, no loadmanagement controls are needed and the decoder 203 is also disconnected.When the independent occupant control 206 connects the light fixtures tothe supply line, the decoders 203 are also connected. This allowsdecoders 203 to receive command signals on the supply line.Consequently, the PCLC system is able execute load management controls.This is particularly helpful when an occupant forgets to disconnect thelight fixtures 205 via the independent occupant control 206.

FIG. 2 also illustrates another important advantage of the PCLC system.That is, PCLC can be adapted to operate with varying types of lightfixtures. As shown in FIG. 2, lighting branches often include differenttypes of light fixtures 205. For example, FIG. 2 includes both 0-10 voltanalog lighting ballasts as well as LED drivers. PCLC can be adapted tooperate with both. In fact, only the decoder needs modification in orderto operate with varying types of light fixtures 205. Examples of how thedecoder 203 can be modified to operate with different light fixtureswill be described below.

The injectors 101, 201 described with reference to FIG. 1 and FIG. 2above can be implemented in a number of ways. FIG. 3 is a schematic foran injector circuit in accordance with one aspect of the invention. Thisnetwork topography temporarily injects an asymmetrical connection ofsilicon power diodes 302, 303, 304, 305, 306 in the AC line conductor.An electro-mechanical relay 301 is used to connect the injectorcircuitry to the AC line conductor. When the relay contacts that shuntthe injector circuitry are momentarily opened, an asymmetrical controlsignal is introduced on the AC line conductor. Power losses will occuronly during this brief interval. Otherwise the injector circuitryconsumes no electrical power. Although an electro-mechanical relay 301has been described in this embodiment, the same switching functionalitycould be obtained with a solid-state relay. Such devices typicallyemploy back-to-back MOSFET or IGBT switching elements, which have verylow conduction voltage drops.

The network used in this embodiment has two parallel branches, onebranch having multiple series-connected diodes, 302, 303, 304, 305 and306, to serve as a current path to the load for one direction and theparallel branch having a single diode 307 producing a lower voltage dropto the load for the other polarity of the AC voltage alternation. Analternating current flowing through this network experiences a typicalvoltage drop of:

-   -   V=n 0.65-volts (where N is the number of diodes in the multiple        diode leg)        and a single 0.65 voltage drop in the other direction. The net        result is to introduce an approximate (n−1)*0.65-volt average DC        component to the supply voltage that is conducted over the        lighting supply branch. The DC voltage drop, or voltage offset,        is within a range that causes approximately 1% or less total        harmonic distortion of the power signal. Preferably, the DC        voltage offset is in the range of 1 to 5 volts. 1 to 5 volts is        large enough to achieve adequate signaling in the presence of        interfering noise without significant power quality depreciation        during the signaling intervals.

Silicon diodes are preferred for implementing this embodiment becausethey are low in cost, readily available, and offer high current ratings.High current ratings are important because all of the current suppliedto the downstream loads will flow through this network. For example, anetwork containing a branch with a 15 ampere lighting load will have todissipate a momentary loss of several watts. Increasing the number ofdiodes to increase the DC value of the offset may seem like anattractive design tactic, but doing so will further increase thedissipative loss.

The injector is preferably installed in locations where the power linesare not otherwise corrupted with loads that can produce an extraneous DCvoltage offset. Typically, the presence of such loads in mostwell-engineered buildings would not be acceptable. In any case, thestandard installation practice for dedicated load lighting is toseparately power the supply branches independently from plug loads andfrom other machinery. Lighting branch power quality is further enhanceddue to the fact that modern electronic ballasts are mandated to includepower factor correction circuitry. These factors help isolate thelighting branch from sources of power quality corruption, that couldotherwise create interfering noise that might interfere with the encodedcontrol.

FIG. 4 is a schematic depicting injector circuitry in accordance withanother aspect of the invention. An electro-mechanical relay 401 is usedto connect the injector circuitry to the AC line conductor. For thisinjector circuit, the branch containing multiple power diodes isreplaced with a junction transistor 402 having its base controlled by alow power Zener diode 403 and a resistor 404. A diode 405 is stillpreferably used to produce a lower voltage drop in the polarity oppositeof that produced by the junction transistor 402. This circuitconfiguration conveniently consolidates all the power losses of themultiple-drop branch into a single readily available junction transistor402. Here, the Zener diode 403 current is only a fraction of the loadcurrent, since it is effectively multiplied by the current gain of thejunction transistor 402. Although a junction transistor 402 isillustrated, either a MOSFET or IGBT could be employed to provide theactive current gain required for the operation of the circuit. Thisembodiment is beneficial because it tends to be a more cost-effectiveoption.

Similar to the embodiment depicted in FIG. 1, an electro-mechanicalrelay 401 is used to connect the injector circuitry to the AC lineconductor. Although an electro-mechanical relay has been described inthis embodiment, the same switching functionality could be obtained witha solid-state relay. Such devices typically employ back-to-back MOSFETor IGBT switching elements, which have very low conduction voltagedrops.

FIG. 5 is a schematic for an injector in accordance with another aspectof the invention. An electro-mechanical relay 505 is used to connect theinjector circuitry to the AC line conductor. For the injector circuitdepicted in FIG. 5, a silicon controlled rectifier (SCR) or abidirectional triode thyristor (TRIAC) 501 is used to provide aunidirectional voltage drop. A diode 504 is preferably used to produce alower voltage drop in the polarity opposite of that produced by theTRIAC or SCR 501. The network consisting of resistor 502 and capacitor503 provides excitation for the silicon controlled rectifier's 501 gateto trigger conduction, and imposes a slight phase delay. This delayreduces the unidirectional conduction angle, thus producing the desiredDC offset. This embodiment is an attractive option because it containswidely available components in the appropriate voltage and currentratings.

FIG. 6 is a schematic for an injector in accordance with yet anotheraspect of the invention. This injector circuit is comprised of not one,but two asymmetrical diode networks. Diode network 603 is configured toproduce an average voltage offset in one polarity, while diode network604 is configured to produce an average voltage offset in the oppositepolarity. Each of the asymmetrical networks is shunted by a normallyclosed switch 601, 602. If switch 601 is momentarily opened, an averagevoltage offset of the appropriate polarity will be produced at the lineout terminal during the actuation interval. Alternatively, if switch 602is momentarily operated, an offset of the opposite polarity will resultduring the actuation interval. This injector configuration is referredto as a bi-polar injector. It may be applied in circumstances wherecomplicated encoding is not desired. For example, this embodiment couldbe applied to produce a rudimentary “dim up” and “dim down” wall controlwithout the needing a complex system control.

The decoders 103, 203 described with reference to FIG. 1 and FIG. 2above can also be implemented in a number of ways. FIG. 7 is a schematicfor a decoder used to detect the presence of control signals on an ACpower line in accordance with an exemplary embodiment.

The decoder in FIG. 7 utilizes an initial “Twin Tee” notch filter toattenuate the 60 (or 50) Hz power line frequency component. The notchfilter is comprised of capacitors 702, 703 and 706, as well as resistors701, 705 and 704. The “Twin Tee” notch filter is followed by a 2-polelow pass filter to further enhance detection of control signals in theform of momentary intervals of DC offset on the powerline. The 2-polelow pass filter is comprised of resistors 707 and 708 and capacitors 709and 710. Transistor inverters 711 and 712 combined with resistors 713,714 and 715 perform impedance transformation and level shiftingfunctions. Resistor 717, diodes 719, 720 and 722, and capacitors 718 and721 serve as an energy-efficient, transformer-less, low-current powersupply. Resistor 723 limits current to microprocessor 716 pin 6, andcapacitor 724 filters high frequency noise. Once the passive filteringdescribed above has extracted the low-frequency data waveform from thepowerline, the signal is presented to microprocessor 716. Microprocessor716 performs several functions, one of which is an adaptive levelslicing demodulation function. This function can be used to extract thecontrol information on the powerline.

FIG. 8 shows a method that can be used by microprocessor 716 to decodecontrol signals on the powerline. The method begins by calculating theaverage DC bias component on the powerline when no control signal ispresent (step 810). From this average, a pulse threshold is determined(step 820). The pulse threshold may be, for example, the average valuebetween the amplitude of a control signal pulse and the average DC biascomponent calculated in step 810. Averaging the threshold value in thismanner provides a reliable way in which to determine a threshold valueabove the background noise level. Once the pulse threshold has beencalculated, the microprocessor can then monitor the DC bias present onthe powerline in order to detect control pulses (step 830). If themicroprocessor 716 detects a pulse signal greater than the thresholdvalue (step 840), the microprocessor 716 will then measure the durationof that pulse (step 850). Once the duration of the pulse signal has beendetermined, the microprocessor 716 will compare the pulse durationmeasurement to a predetermined pulse duration threshold (step 860). Ifthe pulse duration exceeds the pulse duration threshold value, themicroprocessor 716 will demodulate the pulse signal into controlinformation based on the selected modulation scheme for the PCLC system.

It should be appreciated that the control information can be modulatedin a number of ways. For example, the control information could bemodulated in a two-state scheme or a multi-level scheme. Two-stateschemes are used for basic on/off functionality. In a two-state scheme,any pulse that has a duration longer than a predetermined value, forexample 500 ms, is considered an “off” signal, while any pulse shorterthan the predetermined value—but still longer than the pulse durationthreshold—is considered an “on” signal. A two-state scheme could also beimplemented where longer pulses are “on” signals and shorter pulses are“off” signals. A multi-level scheme preferably uses pulses of a fixedwidth, for example 200 ms, and varies the time between the pulses tosend multiple bits of binary data. The number of discernable timeperiods between pulses represents the number of bits of data being sent.

It is important that the decoder circuit be capable of certification forlisting by Underwriters Laboratories® (UL) and other internationalsafety organizations. Thus, the output from the decoder circuit ispreferably isolated from the powerline. FIG. 9 shows an isolationcircuit used to isolate the decoder output from the powerline inaccordance with on aspect of the invention. The output from pins 3 and 4of microprocessor 716 are fed to optocoupler 901, which provides thenecessary isolation. In turn, optocoupler 901 is connected to aset-reset flip-flop gate created by logic gates 902 and 903 andresistors 904 and 905. Resistor 910 and capacitor 907 filter noise fromthe set-reset flip-flop output. Based upon output from the optocoupler,the set-reset flip-flop gate sends short, low-power trigger pulses toproduce a low frequency, pulse-width-modulated source for the dimmingcontrol signal. The dimming control signal is connected to the dimmingcontrol in the light fixture. Voltage regulator 906 is used to step downthe supply voltage from the light fixture in order to power theset-reset flip-flop gate. Capacitors 908 and 909 filter noise from thevoltage regulator circuit. This galvanic barrier circuitry is poweredfrom an isolated source of voltage in the fluorescent ballast or LEDdriver to which it is connected.

The decoder is designed to operate with a number of well-known lightingfixtures. For instance, remote control of low voltage LED loads iseasily accomplished with PCLC technology. The drivers used to energizeLED loads conveniently have low voltage outputs that can serve to powera decoder as well as the LED load. This is not only cost-effective, butit also simplifies the complexity of UL/CE® certification. Severaldifferent possible arrangements are presented that are applicable tocommercial LED drivers that incorporate either constant current orconstant voltage output regulation. In the case of constant voltage,dimming functionality can be added to a driver that does not otherwisehave dimming functionality. An external pulse width modulation (“PWM”)switch interrupts a variable percentage of the drive current in order todim the LED load. Either continuous or multi-step dimming is possiblewith the same hardware configuration, differing only by the decoder'smicroprocessor firmware. Constant current drivers must include a dimmingfunction if they are to be controlled by a decoder. Dimming constantcurrent drivers often use a PWM digital input that is used to change theduty cycle of the current source located within the driver circuitry.

FIG. 10 is a block diagram for a configuration for adapting PCLC to alight fixture using a 0-10 volt analog ballast or voltage-controlleddimming LED driver. In this configuration, the decoder includes amicroprocessor 1001, a voltage regulator 1002 and an isolated lineinterface 1003. The line interface 1003 is configured to isolate themicroprocessor 1001 from the powerline. The voltage regulator 1002included in this configuration is also isolated from the power line inorder to meet UL® certification standards. Here, the microprocessor 1001supplies a 0-10 volt output that can be used to control devices thatlack an internal current source 1004, such as a fluorescent light. Thisconfiguration can produce either multiple step or continuous loadcontrol, depending on the firmware loaded into the microprocessor 1001.This configuration has no artificial lower limits to its control range.It is able to take advantage of the full control range (e.g. 5-100%) ofthe load to which it is connected.

FIG. 11 is a block diagram for installing a decoder in a lightingfixture that utilizes a PWM controlled dimming LED driver or currentcontrol. In this configuration, the decoder includes a microprocessor1101, an isolated line interface 1103 and a voltage regulator 1102. Theisolated line interface 1103 isolates the microprocessor 1101 from thepowerline. The voltage regulator 1102 is also isolated from thepowerline order to meet UL® certification standards. The microprocessor1101 produces a variable duty-cycle PWM signal that controls the LED1104 intensity. It results in continuous or step-incremented changes inthe luminous output of the controlled LEDs 1104. Typically, thefrequency of the PWM control signal is 100 to 500 hertz to minimizeperceptible flicker and stroboscopic effects.

The decoder can also be configured to operate with light fixtures usingtwo-wire dimming fluorescent ballasts. These ballasts have become apopular choice for retrofit applications because they offer the abilityto add dimming control over existing power wiring. They also operatewith many standard wall dimmer controls in a way that is familiar toboth occupants and the installation trades. Similarly, it appears thatthe same type of dimmer controls are finding wider acceptance for theemerging application of LED dimming. In some instances, it may bedesirable to have a few 2-wire dimming loads fed by a branch circuitthat also serves non-dimming loads. FIG. 12 is a block diagramillustrating how PCLC can be adapted to mixed load, two-wire dimmingballasts.

The decoder configuration in FIG. 12 includes a microprocessor 1201, avoltage regulator 1202, and a line interface 1203. The voltage regulatorreceives power from the branch supply line. Line interface 1203 ensuresthat the decoder is isolated from the power line for certificationpurposes. The microprocessor 1201 receives control signals sent on thepower line, and decodes them into the appropriate load managementcontrols. The microprocessor then controls the TRIAC dimmer 1204 whichlimits power to the controlled the load 1205.

In addition to two-wire dimming ballasts, the decoder can also beadapted to operate with three-wire dimming ballasts. In its normalapplication, the third wire of three-wire dimming ballasts emanates froma conventional phase-cut wall dimmer that is connected in tandem to eachcontrolled load. This third wire carries only dimming information butnot the excitation for the ballast. This reduces the amount of powerquality degradation that is introduced from the dimmed load and permitsdimming down to very low levels. Instead of using a third wire fordimming commands, PCLC recovers the commands sent over the power line,as shown in FIG. 13.

The decoder configuration in FIG. 13 is very similar to the decoderconfiguration of FIG. 12. It consists of a microprocessor 1301, avoltage regulator 1302, and a line interface 1303. Here, the decoderconfiguration replaces a conventional phase-cut wall dimmer that isconnected in tandem the load. The voltage regulator receives power fromthe branch supply line. Line interface 1303 ensures that the decoder isisolated from the power line for certification purposes. Themicroprocessor 1301 receives control signals sent on the power line, asopposed to signals coming from the phase-cut wall dimmer, and decodesthem into the appropriate load management controls. The microprocessorcontrols operation of the TRIAC dimmer 1304 used to control the load1305.

PCLC can also be adapted for use in ballasts or drivers implementing aDigital Addressable Lighting Interface (“DALI”). FIG. 14 is a blockdiagram for a decoder configured to operate with a light fixture that isequipped with a DALI control input. This configuration consists of amicroprocessor 1401 programmed with specific DALI commands, a switchinguniversal voltage supply 1402, and a line interface 1403. Typically,this variety of control would be used in an addressable network spanninga large number of independent zones. However, in a non-networkedapplication, only one ballast or driver is being controlled.Consequently, the decoder can take advantage of a special DALI routine,designated as “broadcast mode.” This routine transmits commands that aredirected to any connected ballast or driver, regardless of its addresssetting. These commands are transmitted in a simplex mode, which doesnot require the return of an acknowledgement.

Because DALI commands transmitted in “broadcast mode” do not require areturn acknowledgement, the microprocessor 1401 can receive the commandsand convert them into dimming commands for light fixture. Preferably,the microprocessor 1401 has a random access memory with a sequence ofpermanently coded DALI commands representing the graduated range ofdimming commands. The microprocessor 1401 sends the appropriate commandto the load with the DALI control input 1404. It is even possible toimplement on/off functionality in this configuration by using the lowestdimming level to turn off the load. PCLC adapted to operate with a lightfixture having a DALI control input is capable of producing the largest(and most apparent) incremental reduction in a managed load.

The decoder for this embodiment may be designed to utilize eithersolid-state (wet contact) or electro-mechanical (dry contact) load relayswitches. In the electro-mechanical relay case, either pulse-actuated orcontinuously energized types can be employed. Pulse actuated relays areconsidered preferable from an energy conservation basis, due to the factthat they consume power only when changing switching state. Solid-staterelays may also be used. Their relatively low holding currents make themefficient from an energy loss standpoint. The random phase switchingvariety of solid-state relay is preferable because it does not exhibittriggering anomalies due to holding current complications.

With the above, a system and method for controlling electrical loadsover an AC powerline is provided.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that the presentinvention be limited only by the claims and the equivalents thereof.

1. A system for transmitting communication signals, the systemcomprising: an injector circuit connected to a powered circuit conductorand configured to modulate a power signal with a direct current voltageoffset, the direct current voltage offset being within a range thatcauses approximately 1 percent or less total harmonic distortion of thepower signal; and a decoder connected to the powered circuit conductorand a load, the decoder configured to demodulate the direct currentvoltage offset to control the load.
 2. The system of claim 1, whereinthe direct current voltage offset is within the range of approximately 1to 5 volts.
 3. The system of claim 1, further comprising a systemcontrol module in communication with the injector circuit, the systemcontrol module configured to connect or disconnect the injector circuitfrom the powered circuit conductor according to a modulation scheme. 4.The system of claim 3, wherein the system control module is wirelesslyconnected to the injector circuit.
 5. The system of claim 3, wherein themodulation scheme is a two-state scheme.
 6. The system of claim 3,wherein the modulation scheme is a multi-level scheme.
 7. The system ofclaim 1, wherein the injector circuit is an asymmetrical network.
 8. Thesystem of claim 7, wherein the asymmetrical network modulates the powersignal with the direct current voltage offset, the direct currentvoltage offset having a first voltage offset for modulating a firstpolarity of the power signal and a second voltage offset for modulatinga second polarity of the power signal, the first voltage offset beingdifferent than the second voltage offset.
 9. The system of claim 8,wherein the first voltage offset is greater than the second voltageoffset.
 10. The system of claim 7, wherein the asymmetrical networkcomprises a transistor configured to produce the first voltage offset inthe first polarity; and a diode configured to produce the second voltageoffset in the second polarity.
 11. The system of claim 7, wherein theasymmetrical network comprises a rectifier circuit configured to producethe first voltage offset in the first polarity; and a diode configuredto produce the second voltage offset in the second polarity.
 12. Thesystem of claim 1, wherein the injector circuit includes a firstasymmetrical network and a second asymmetrical network.
 13. The systemof claim 12, wherein the first asymmetrical network is configured tomodulate the power signal with the direct current voltage offset toproduce a first average voltage offset in a first polarity of the powersignal, and the second asymmetrical network is configured to modulatethe power signal with the direct current voltage offset to produce asecond average voltage offset in a second polarity of the power signal,the first average voltage offset being opposite to the second averagevoltage offset.
 14. The system of claim 1, further comprising anisolation interface configured to provide galvanic isolation between thepowered circuit conductor and the decoder.
 15. The system of claim 1,wherein the decoder includes a microprocessor configured to demodulatethe direct current voltage offset to control the load.
 16. The system ofclaim 15, wherein the microprocessor is configured to demodulate thedirect current voltage offset on the powered circuit conductor bycalculating an average direct current voltage offset of the powersignal, measuring a direct current voltage offset of the power signal,comparing the direct current voltage offset of the power signal to theaverage direct current voltage offset of the power signal, andconverting the direct current voltage offset of the power signal to acontrol signal for controlling the load when the direct current voltageoffset of the power signal is greater than the average direct currentvoltage offset of the power signal.
 17. A method for transmittingcommunication signals, the method comprising: modulating a power signalon a powered circuit conductor with a direct current voltage offset, thedirect current voltage offset being within a range that causesapproximately 1 percent or less total harmonic distortion of the powersignal; and demodulating the direct current voltage offset to control aload.
 18. The method of claim 17, wherein the direct current voltageoffset is within the range of approximately 1 to 5 volts.
 19. The methodof claim 17, further comprising modulating the power signal in a pulsepattern.
 20. The method of claim 17, further comprising controllingmodulation of the power signal with a control module, according to amodulation scheme.
 21. The method of claim 20, wherein the modulationscheme is a two-state scheme.
 22. The method of claim 20, wherein themodulation scheme is a multi-level scheme.
 23. The method of claim 17,further comprising providing galvanic isolation for the powered circuitconductor.
 24. The method of claim 17, wherein demodulating the directcurrent voltage offset to control the load comprises: calculating anaverage direct current voltage offset of the power signal; measuring adirect current voltage offset of the power signal; comparing the directcurrent voltage offset of the power signal to the average direct currentvoltage offset of the power signal; and converting the direct currentvoltage offset of the power signal to a control signal for controllingthe load when the direct current voltage offset of the power signal isgreater than the average direct current voltage offset of the powersignal.